ZOANTHARIA 



nematocysts may change their form a little in the different liqtiids of preservation, these capsules may 

 nevertheless be considered resistant on the whole. This is also indicated by tiie agreement in 

 numbers I obtained in species where a large material was examined. It seems to me at any rate, 

 that data regarding the structure, size and distribution of the nematocysts must be taken into con- 

 sideration in the characterisation of the different forms of Zoanthidae. Such data may often give 

 reliable information as to whether we have a constant species before us and are at any rate for the 

 sake of control of great value. 



The arrangement, size and structure of the nenuitocysts have been examined in preparations 

 embedded in glycerine diluted with water. As to the filaments it is generally very difficult to separate 

 them from other parts of the mesentery. Parts of these break loose when the filaments are removed. 

 We might imagine, therefore, that the nematocysts are not always lying in the filament but in other 

 parts of the mesentery. This does not seem however — at any rate not as a rule — to be the case, 

 as I have found none of the capsules characteristic of the species in sections of the non-filamentous 

 part of the mesenteries. There are exception to this rule however, to be mentioned later in the 

 present paper. In a bottle with 6 colonies of Epizoanthus incrustatus from the neighbourhood of 

 Iceland I found that two of the colonies had some peculiar, egg-shaped nematocysts in the mesenteries, 

 which were not present in the other colonies from the same locality. At first sight I thought I had 

 another species before me or at any rate a variety-, but as I could find no other characters separating 

 these colonies from the normal ones, I had to look for another explanation. This was soon obtained, 

 all the sooner because it struck me in the first examination that these nematocysts closely resembled 

 the nematocysts of Hydrozoa. In this case they should not lie in the filament itself but inside this 

 in the entoderm. On closer examination of the section this was found to be correct. The egg-shaped 

 capsules have thus undoubtedly been taken in together with the food. I have found the same kind 

 of nematocysts in a colony of Epizoanthus erdmanni also from Iceland. Even in this colony the 

 capsules seemed to be lying in the entodermal part of the mesentery, though the fixing was hardly 

 so good here that they could be said with absolute certainty to be found in the entoderm only. If 

 this kind of unusual capsule occurs in the filament, especially if onl>' in certain specimens of a species, 

 there is reason to suspect that we are dealing with capsules that have penetrated into the animal 

 from without and not a normal component. I think it necessary to point this out specially for the 

 sake of future investigations. 



In all the specimens examined by me the nematocysts are almost always arranged in the same 

 way. In the ectoderm of the coenenchyme and of the body-wall only nematocysts with greatly twisted 

 thread are found. Regarding the distribution of the nematocysts in the body wall, they are most 

 numerous in the proximal part, in the capitular region they are scarce or absent Yet sometimes the 

 nematoc)st-capsules there are more numerous and of a different size and appearance than in the other 

 parts of the body-wall. In the ectoderm of the tentacles there are alwa>s extremely numerous 

 spirocysts (thin-walled capsules), less numerous typical, thick-walled capsules, sometimes similar capsules 

 as in the body-wall, though never abundantly. 



The oral disc shows, in the few cases I have examined this, the same distribution of the 

 capsules as occurs in the tentacles. In the oesophagus there is mostly thick-walled capsules, in some 



